Center for Innovation in Global Health Technologies (CIGHT), Department of Biomedical Engineering, Northwestern University, Evanston, IL, 60208, USA.
Sci Rep. 2017 Jun 16;7(1):3653. doi: 10.1038/s41598-017-03930-3.
Nucleic acid amplification tests are increasingly used to diagnose tuberculosis (TB) due to their speed and sensitivity compared to sputum smear microscopy. However, these tests fail to equal culture's sensitivity with sputum smear microscopy negative specimens and therefore cannot be used to rule out TB disease. For molecular tests to match culture's sensitivity, they must detect ≤10 genomic copies of Mycobacterium tuberculosis (MTB) DNA, the limit of detection of culture, process ≥1 ml of sputum ensuring sufficient number of MTB are in the reaction, and efficiently remove sputum associated inhibitors from this large sample. Here we report the preliminary characterization of XtracTB Assay, a MTB testing protocol designed for inclusion in either an integrated point-of-care platform or a high throughput automated central laboratory system. The test combines DNA sequence specific sample prep to reduce the co-extraction of qPCR inhibitors with the amplification of two MTB specific loci (IS6110 and senX3-regX3) to increase test sensitivity and minimize the likelihood of false negatives. The analytical sensitivity of the XtracTB Assay was 5 genomic copies/ml of sputum rivaling that of culture. Furthermore, 142 valid test results yield clinical sensitivity of 94.9% (95% CI: 90.1-99.9) and specificity of 100% (95% CI: 90.0-100.0).
核酸扩增检测由于其速度和灵敏度，与痰涂片显微镜检查相比，越来越多地用于诊断结核病 (TB)。然而，这些检测未能与痰涂片显微镜检查阴性标本的培养物的灵敏度相匹配，因此不能用于排除结核病。为了使分子检测与培养物的灵敏度相匹配，它们必须检测到≤10 个结核分枝杆菌 (MTB) DNA 的基因组拷贝，这是培养物的检测极限，处理≥1ml 的痰液以确保有足够数量的 MTB 进入反应，并且从这个大样本中有效地去除与痰液相关的抑制剂。在这里，我们报告了 XtracTB 检测的初步特征，这是一种为纳入即时护理平台或高通量自动化中央实验室系统而设计的 MTB 检测方案。该测试结合了 DNA 序列特异性样本制备，以减少 qPCR 抑制剂的共提取，同时扩增两个 MTB 特异性基因座 (IS6110 和 senX3-regX3)，以提高测试灵敏度并最大程度地减少假阴性的可能性。XtracTB 检测的分析灵敏度为 5 个基因组拷贝/ml 的痰液，与培养物相当。此外，142 个有效测试结果得出临床灵敏度为 94.9%（95%CI：90.1-99.9），特异性为 100%（95%CI：90.0-100.0）。
